Limited predictive value of preoperative nigrosome integrity for motor outcomes in Parkinson’s disease deep brain stimulation

Nigrosome-1, a substructure in the dorsolateral substantia nigra, is characterized by the "swallow tail sign" (STS)-a dorsolateral nigral hyperintensity (DNH)-on susceptibility-weighted MRI in healthy individuals. Loss of the STS reflects degeneration of nigrosome-1 and serves as a recognized diagnostic marker for Parkinson's disease (PD). However, its value in predicting disease severity and deep brain stimulation (DBS) outcomes remains unclear. We retrospectively analyzed 27 PD patients who underwent 3 T susceptibility map-weighted imaging (SMWI) derived from quantitative susceptibility mapping (QSM) prior to DBS. Nigrosome integrity was graded on a four-point scale, and patients were grouped as fully abnormal (Grade 4) or non-fully abnormal (Grades 1-3). No significant group differences were found in baseline motor severity or postoperative improvement, although the non-fully abnormal group showed lower absolute postoperative UPDRS III scores. Nigrosome grading showed no consistent association with symptom lateralization, including contralateral tremor severity or DBS responsiveness. These findings suggest that nigrosome integrity assessed by SMWI MRI-while a validated diagnostic biomarker for PD-showed no moderate-to-large effects with either disease severity or DBS outcomes. Although small effects cannot be excluded, their clinical relevance would be uncertain. Nigral imaging should be interpreted within a broader multimodal framework including clinical, imaging, and biochemical data.